ATMEGA32 View Datasheet(PDF) - Atmel Corporation
Part Name
Description
MFG CO.
'ATMEGA32' PDF : 346 Pages View PDF
ATmega32(L)
Calibrated Internal RC
Oscillator
Table 7. External RC Oscillator Operating Modes
CKSEL3..0
Frequency Range (MHz)
0101
0110
0.1 - 0.9
0.9 - 3.0
0111
3.0 - 8.0
1000
8.0 - 12.0
When this Oscillator is selected, start-up times are determined by the SUT fuses as
shown in Table 8.
Table 8. Start-up Times for the External RC Oscillator Clock Selection
SUT1..0
00
Start-up Time from
Power-down and
Power-save
18 CK
Additional Delay
from Reset
(VCC = 5.0V)
–
Recommended Usage
BOD enabled
01
18 CK
4.1 ms
Fast rising power
10
18 CK
11
6 CK(1)
65 ms
4.1 ms
Slowly rising power
Fast rising power or BOD enabled
Note: 1. This option should not be used when operating close to the maximum frequency of
the device.
The Calibrated Internal RC Oscillator provides a fixed 1.0, 2.0, 4.0, or 8.0 MHz clock. All
frequencies are nominal values at 5V and 25°C. This clock may be selected as the sys-
tem clock by programming the CKSEL fuses as shown in Table 9. If selected, it will
operate with no external components. The CKOPT Fuse should always be unpro-
grammed when using this clock option. During Reset, hardware loads the calibration
byte for the 1MHz into the OSCCAL Register and thereby automatically calibrates the
RC Oscillator. At 5V, 25°C and 1.0 MHz Oscillator frequency selected, this calibration
gives a frequency within ± 3% of the nominal frequency. Using calibration methods as
described in application notes available at www.atmel.com/avr it is possible to achieve ±
1% accuracy at any given VCC and Temperature. When this Oscillator is used as the
Chip Clock, the Watchdog Oscillator will still be used for the Watchdog Timer and for the
reset time-out. For more information on the pre-programmed calibration value, see the
section “Calibration Byte” on page 258.
Table 9. Internal Calibrated RC Oscillator Operating Modes
CKSEL3..0
0001(1)
Nominal Frequency (MHz)
1.0
0010
2.0
0011
4.0
0100
8.0
Note: 1. The device is shipped with this option selected.
29
2503J–AVR–10/06
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